Stator and rotor design for periodic torque requirements

ABSTRACT

Disclosed is a motor or generator comprises a rotor and a stator, wherein the rotor has an axis of rotation and is configured to generate first magnetic flux parallel to the axis of rotation, the stator is configured to generate second magnetic flux parallel to the axis of rotation, and at least one of the rotor or the stator is configured to generate a magnetic flux profile that is non-uniformly distributed about the axis of rotation. Also disclosed is a method that involves arranging one or more magnetic flux producing windings of a stator non-uniformly about an axis of rotation of a rotor of an axial flux motor or generator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. § 119(e) of U.S.Provisional Application Ser. No. 62/754,051, entitled PLANAR STATOR ANDROTOR DESIGN FOR PERIODIC TORQUE REQUIREMENTS, filed Nov. 1, 2018. Thisapplication is also a continuation-in-part and claims the benefit under35 U.S.C. § 120 to U.S. patent application Ser. No. 15/983,985, entitledPRE-WARPED ROTORS FOR CONTROL OF MAGNET-STATOR GAP IN AXIAL FLUXMACHINES, filed May 18, 2018, and published as U.S. Patent ApplicationPub. No. US 2018/0351441, which claims the benefit under 35 U.S.C. §119(e) to each of (1) U.S. Provisional Patent Application Ser. No.62/515,251, entitled PRE-WARPED ROTORS FOR CONTROL OF MAGNET-STATOR GAPIN AXIAL FLUX MACHINES, filed Jun. 5, 2017, and (2) U.S. ProvisionalPatent Application Ser. No. 62/515,256, entitled AIR CIRCULATION INAXIAL FLUX MACHINES, filed Jun. 5, 2017. The contents of each of theforegoing applications, publications, and patents are herebyincorporated herein, by reference, in their entireties, for allpurposes.

BACKGROUND

Permanent magnet axial flux motors and generators described by severalpatents, including U.S. Pat. No. 7,109,625 (“the '625 patent”), featurea generally planar printed circuit board stator (PCS) interposed betweenmagnets featuring alternating north-south poles. These printed circuitboard stators, when supported to the fixed frame from the outside edgeof the stator, have a hole through which the shaft linking the rotorspasses. An alternate embodiment is to interchange roles of the inner andouter radius, resulting in a situation where the inner radius of thestator is supported, and the rotor envelopes the stator. The shaft iseffectively moved to the outer radius in this configuration, sometimescalled an “out-runner.”

BRIEF DESCRIPTION OF THE DRAWINGS

Objects, aspects, features, and advantages of embodiments disclosedherein will become more fully apparent from the following detaileddescription, the appended claims, and the accompanying figures in whichlike reference numerals identify similar or identical elements.Reference numerals that are introduced in the specification inassociation with a figure may be repeated in one or more subsequentfigures without additional description in the specification in order toprovide context for other features, and not every element may be labeledin every figure. The drawings are not necessarily to scale, emphasisinstead being placed upon illustrating embodiments, principles andconcepts. The drawings are not intended to limit the scope of the claimsincluded herewith.

FIG. 1A shows an example of an axial flux motor or generator with whichsome aspects of this disclosure may be employed;

FIG. 1B is an expanded view showing the components of the axial fluxmotor or generator shown in FIG. 1A and a means for assembling suchcomponents;

FIG. 2 is a conceptual diagram showing three printed circuit boardstators having equal areas but different configurations;

FIG. 3 is a diagram showing how multiple stator segments may be arrangedfor manufacture on a printed circuit board panel of standard dimensions;

FIG. 4 is a diagram showing how a subset of the stator segments shown inFIG. 3 would appear if they were arranged edge to edge on the circuitboard panel shown in FIG. 3 ;

FIG. 5 shows an example arrangement of a stator segment with respect tomagnets on a rotor in accordance with some aspects of the presentdisclosure;

FIG. 6 shows the same arrangement as FIG. 5 , but where the rotor isshown at an angle where the stator segment overlaps with a magnetsection that provides peak torque;

FIG. 7 shows an example arrangement of multiple stator segments withrespect to magnets on a rotor in accordance with some aspects of thepresent disclosure; and

FIG. 8 illustrates a cross section of an example embodiment of an axialflux motor that is configured and integrated with a washing machine loadin accordance with some aspects of the present disclosure.

SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features, nor is it intended to limit the scope of the claimsincluded herewith.

In some of the disclosed embodiments, a motor or generator comprises arotor and a stator, wherein the rotor has an axis of rotation and isconfigured to generate first magnetic flux parallel to the axis ofrotation, the stator is configured to generate second magnetic fluxparallel to the axis of rotation, and at least one of the rotor or thestator is configured to generate a magnetic flux profile that isnon-uniformly distributed about the axis of rotation.

In other disclosed embodiments, a method involves arranging one or moremagnetic flux producing windings of a stator non-uniformly about an axisof rotation of a rotor of an axial flux motor or generator.

In yet other disclosed embodiments, a rotor for use in a motor orgenerator comprises a support structure and one or more magnet segmentsthat are supported by the support structure and that generate firstmagnetic flux parallel to an axis of rotation about which the supportstructure rotates when assembled with a stator that generates secondmagnetic flux parallel to the axis of rotation, wherein the one or moremagnet segments are configured and arranged to generate a magnetic fluxprofile that is non-uniformly distributed about the axis of rotation.

DETAILED DESCRIPTION

In existing axial flux motors or generators, such as those disclosed inU.S. Pat. Nos. 7,109,625; 9,673,688; 9,800,109; 9,673,684; and10,170,953, as well as U.S. Patent Application Publication No.2018-0351441 A1 (“the '441 Publication”), the entire contents of each ofwhich are incorporated herein by reference, the magnetic flux generatingcomponents of the stator, whether comprised of a single continuousprinted circuit board or multiple printed circuit board segments, arearranged such that, at any given time when the windings of the statorare energized with current, the locations of peak magnetic fluxgenerated by the stator are distributed uniformly with respect to theangle about the rotor's axis of rotation. Similarly, in such machines,the magnetic flux generating components of the rotor, whether comprisedof a ring magnet or individual magnets disposed in pockets, are alsoarranged such that, at any given point in time, the locations of peakmagnetic flux generated by the rotor are likewise distributed uniformlywith respect to angle about the rotor's axis of rotation. Accordingly,in all such machines, at any given time the machine is in operation, thelocations of peak magnetic flux generated by each of the rotor and thestator are uniformly distributed as a function of angle about themachine's axis of rotation. In other words, for each of the rotor andthe stator in such machines, the same angle separates each location ofpeak magnetic flux from the next adjacent location of peak magnetic fluxabout the axis of rotation so that that the magnetic flux profile ofeach of the rotor and the stator are uniformly distributed about theaxis of rotation.

Disclosed herein are alternate designs, with advantages in cost relativeto conventional designs for certain loads and machine configurations, inwhich the stator and/or the rotor may instead be configured to have amagnetic flux profile that is non-uniformly distributed about therotor's axis of rotation. In some embodiments, for example, a stator canbe configured so that it describes a fraction ansurrounding theprinciple axis of the machine. If such a stator segment can be located,due to the integration of the machine with the attached load, at a largeradius compared to a stator of equal area distributed uniformly aboutthe same axis, the torque produced may be proportional to the increasein radius at which the stator segment is disposed, assuming equivalentflux in the gap and current density limits in the stator. However, thecost of maintaining equivalent flux in the gap for an “off center”stator segment is an increase in magnet volume inversely proportional tothe angle subtended by that segment. This is not a desirable tradeoff inmost cases. However, in an application where peak torque is desired at aparticular angle or range of shaft angles, the magnet material may bedistributed non-uniformly with respect to the rotor, so that the statoris exposed to peak magnetic flux density at the shaft angles where peaktorque is desired. For generator applications where the source hasperiodic torque production capacity, a machine designed according tothis principle may offer similar advantages.

The design of the stator and magnet system to produce peak torque atspecific angles is not limited to one stator segment and/or oneconcentration of magnetic material on the rotor, although this is thesimplest embodiment. Embodiments including one or more non-uniformlydistributed stator segments and/or one or more non-uniformly distributedmagnet segments may provide useful combinations of torque capability asa function of angle. It should be appreciated that the same or similartorque capability as a function of angle can be achieved using differentcombinations of one or more non-uniformly distributed stator segmentsand one or more non-uniformly distributed magnet segments. For example,the same or similar torque capability as a function of angle can beachieved by interchanging the distribution of stator segments versusrotor magnet locations. This may allow designers to effect tradeoffs inthe cost of magnet material and stator area while achieving the same orsimilar torque capability as a function of angle.

The design of a machine to produce peak torque at a particular angledoes not preclude continuous rotation. When continuous rotation isdesired, a machine designed according to the principles disclosed herecan supply torque in a series of pulses (at the peak torque angles) thatare smoothed by the moment of inertia of the attached load to provideapproximately constant speed. An advantage of this design is that thelosses in the stator due to eddy currents may be zero when the statordoes not overlap the magnets. Another possibility for continuousrotation is to distribute magnets so that the stator segment always seesmagnet flux, but at smaller magnitude than the “peak torque” angles.

Some embodiments described herein may be particularly advantageous forapplications where the machine radius can be significantly increased,relative to a conventional design. In these applications, a planarcircuit board stator (PCS) segment disposed at a larger radius than auniform planar circuit board stator may achieve higher peak torque perunit area of stator. Further, in comparison to a thin annular stator ata large radius, stator segments can be “tiled” or arranged on a printedcircuit board “panel” of standard size. This may allow a more efficientutilization of printed circuit board material and reduce the cost of theassociated machine.

Examples of application areas include reciprocating piston or diaphragmtype pumps, which may have a periodic torque requirement. Also, forpurposes of balance, these machines frequently include an off-centermass that can potentially be replaced by an asymmetrically designedrotor. Similarly, generators coupled to single piston engines maybenefit from co-design of balancing masses with the magnetic materialsin a stator-segment type generator. Other potential applications includewashing machines or other applications where the motor or generatormoves through a limited angle, and periodic or “reversing” type loads.

A basic observation of the novel concepts disclosed herein can bereduced to a “scaling” argument for otherwise equivalent stators orstator segments, independent of the internal organization and connectionof the stator, based on fundamental considerations of the design. In aconventional annular PCS, conforming to the description in the '625patent, the torque can be expressed as followsτ=∫_(r1) ^(r2)∫₀ ^(2π) rdrdθrf _(dens)(r).

The components of this expression include integration from a firstradius r1 to a second radius r2, comprising the active area of thestator. The integral covers a complete annulus by the limits ofintegration on θ. The term r dr dθ is a differential area element, and rf_(dens) is the torque density magnitude corresponding to the equationτ=r×F. The force density is θ-directed due to the axial flux and radialcurrent density, i.e.,f _(dens) =J(r)×B

Here, the force density is the product of the current density supportedby the stator, and magnetic flux density resulting from the rotor magnetcircuit and stator reaction at that current density. For illustration, Bis assumed to be radial. In stators designed according to the '625patent, diverging radial traces effectively introduce a 1/r decrease incurrent density from the inner radius r1. A model capturing this effectisJ(r)=J ₀ r ₁ /r

where J₀ is the maximum supported current density based on theinterference of features at a given copper weight, via size andclearance requirements at the inner radius. With this model,τ_(peak) =J ₀ BAr ₁the current density supported by the stator depends on the number ofinner vias that can be disposed at r1, which is dependent on featuresizes and associated clearances, as well as the circumference at r1, andwhether that circumference accommodates features at a spacing thatapproaches the fabrication limits. Thus, it is not strictly correct toregard J₀ as constant. For r1=0, for example, no vias can beaccommodated, and J₀=0. However, for motors of practical interest, J₀will approach a value dependent primarily on thermal considerations andclearance requirements. Taking J₀ as a constant for purposes ofcomparison between otherwise equivalent stators tends to make aconventional stator located around the central shaft, with a smaller r1,appear more competitive than a stator segment at a larger radius.

The area A of the stator or stator segment with angular extent δ is

$A = {\frac{\delta}{2\pi}{\pi\left( {r_{2}^{2} - r_{1}^{2}} \right)}}$

For a stator of conventional design, δ=2π. For a stator segment, δideally corresponds to a whole number of pole pairs. For purposes ofcomparison between stator segments and conventional designs on the basisof cost, it is reasonable to compare equal-area stators and magnetassemblies. Multiple solutions of δ and r₂ exist for any r₁ as the innerradius r₁ is increased, and considered here as the independent variable.In particular, when considering δ, the pole spacing over a segment neednot also conform to the usual constraint of disposing poles uniformlyover 2π rad, as in a conventional stator. This suggests considerabledesign flexibility for the segment that is not enjoyed by theconventional stator, as well as the ability to achieve equal area A.Examples of advantages of displacing stator area to larger r₁ withcompact δ, include: (1) stator segments with larger r₁ offer higher peaktorque per unit area, (2) when stator segments and magnetic materialoverlap fully at specific rotor angles (or angle ranges), peak torque isavailable, (3) there is no eddy current loss in the machine when themagnetic material and stator do not overlap, (4) stator segments can beobtained where r₁, r₂, and δ are such that the segments can “nest” on aprinted circuit board panel, minimizing wasted material and cost, and(5) peak torque per unit area (or per unit cost) increases with theradius of stator segment.

Given a design procedure for a prototype conventional stator with δ=2πmeeting a specific torque τ_(p), designs for stator segments subtendinga subset of the poles in the prototype design spanning an angle δ can beinferred to produce a peak torque of

$\frac{\delta}{2\pi}\tau_{p}$over the range of angles where the segment fully overlaps the magneticmaterial. Thus, a practical design procedure for segments is to designconventional stator prototypes, where the torque requirement isincreased by the ratio of the poles in the conventional stator relativeto the poles intended to be preserved in the segment. This procedure,while expedient, does not exploit the freedom in the segmented design,because the pole spacing is simultaneously constrained to the angularextent of the segment, and to the 2π extent of the conventional design.The segment angle δ does not need to be a divisor of 2π and can thus beoptimized to meet the design constraints.

Combinations of stator segments and magnetic material, concentrated atparticular angles on the fixed frame and rotor, can achieve varioustorque capabilities as a function of angle. One or more areas on therotor may carry magnetic materials comprising different flux densities,one or more pole pairs, and may be distributed at various angles. Theremay be one or more stator segments, in the fixed frame, positioned atvarious angles.

Examples of motor and/or generator designs in which non-uniformlydistributed stators and/or rotors, such as those disclosed herein, maybe employed are described in U.S. Pat. Nos. 7,109,625; 9,673,688;9,800,109; 9,673,684; and 10,170,953, as well as U.S. Patent ApplicationPublication No. 2018-0351441 A1 (“the '441 Publication”), which areincorporated by reference above. Illustrative examples of such machineswill initially be described in connection with FIGS. 1A and 1B. Examplesof stators and rotors having magnetic flux profiles that arenon-uniformly distributed about a rotor's axis of rotation, and whichmay be employed in such machines, will then be described in connectionwith FIGS. 2-8 .

FIG. 1A shows an example of a system 100 employing a planar compositestator 110 in an assembly with rotor components 104 a and 104 b, shaft108, wires 114, and controller 112. An expanded view showing thesecomponents and a means for their assembly is shown in FIG. 1B. Thepattern of magnetic poles in the permanently magnetized portions 106 a,106 b of the rotor assembly is also evident in the expanded view of FIG.1B. FIG. 1A is an example of an embodiment where the electricalconnections 114 are taken at the outer radius of the PCS 110, and thestator is mounted to a frame or case at the outer periphery. Anotheruseful configuration, the “out-runner” configuration, involves mountingthe stator at the inner radius, making electrical connections 114 at theinner radius, and replacing the shaft 108 with an annular ringseparating the rotor halves. It is also possible to configure the systemwith just one magnet, either 106 a or 106 b, or to interpose multiplestators between successive magnet assemblies. Wires 114 may also conveyinformation about the position of the rotor based on the readings ofHall-effect or similar sensors mounted on the stator. Not shown, butsimilar in purpose, an encoder attached to the shaft 108 may provideposition information to the controller 112.

The system 100 in FIGS. 1A and 1B can function either as a motor, or agenerator, depending on the operation of the controller 112 andcomponents connected to the shaft 108. As a motor system, the controller112 operates switches so that the currents in the stator 110 create atorque about the shaft, due to the magnetic flux in the gap originatingfrom the magnets 104 a, 104 b connected to the shaft 108. Depending onthe design of the controller 112, the magnetic flux in the gap and/orthe position of the rotor may be measured or estimated to operate theswitches to achieve torque output at the shaft 108. As a generatorsystem, a source of mechanical rotational power connected to the shaft108 creates voltage waveforms at the terminals 112 of the stator. Thesevoltages can either be directly applied to a load, or they can berectified with a three-phase (or poly phase) rectifier within thecontroller 112. The rectifier implementation 112 can be“self-commutated” using diodes in generator mode, or can be constructedusing the controlled switches of the motor controller, but operated suchthat the shaft torque opposes the torque provided by the mechanicalsource, and mechanical energy is converted to electrical energy. Thus,an identical configuration in FIG. 1A may function as both a generatorand motor, depending on how the controller 112 is operated.Additionally, the controller 112 may include filter components thatmitigate switching effects, reduce EMI/RFI from the wires 114, reducelosses, and provide additional flexibility in the power supplied to ordelivered from the controller.

FIG. 2 shows geometries of three stators 202, 204, 206 with differentangular and radial extent, but of equal area. Stators 204 and 206 differby the inner radius. Stator 206 shows relative dimensions typical ofstators as described by the '625 patent. Stator 204 is a thin annulardesign. In stator 204, the inner radius is increased, but a stator withthese relative dimensions does not make efficient use of a “panel” ofprinted circuit board material. Stator 202 shows a stator segment 208,as proposed herein, of equal area and equivalent radius to stator 204.All else equal, at the larger radii, stators 202 and 204 would produce ahigher peak torque than stator 206 as the radius increases the torquearm.

FIG. 3 shows the “panelization,” or packing, of stator segments like thesegment 208 shown in FIG. 2 , on a standard sized printed circuit boardpanel 302. The effective utilization of the panel 302 is high with theillustrated arrangement. Cost of the stator segments 208 is inverselyproportional to the utilization of the panel 302.

FIG. 4 shows an ineffective arrangement of segments 208 of the same sizeas in FIG. 3 on the panel 302. While this arrangement is not practical,it shows the effective panel utilization that would be achieved for aconventional stator with the same inner and outer radii as achieved bythe segments 208.

FIG. 5 shows an example arrangement of a stator segment 208 with respectto magnets 502 on a rotor 504. In the illustrated example, a denseangular extent 506 of the magnets 502, also referred to herein as a“dense magnet area,” on the rotor 504 is provided to achieve peak torqueat the angle of overlap with the stator segment 208. Less dense angularextents 508 of the magnets 502, also referred to herein as “less densemagnet areas,” are arranged to provide a lower torque capabilityindependent of angle. Although not illustrated, it should be appreciatedthat, in some embodiments, non-magnetic elements may be added in thevicinity or the less dense magnet areas 508 to balance the weight of therotor 504 as a whole. Further, it should be appreciated that, in someembodiments, an additional rotor portion (not shown) having acorresponding, though opposite polarity, magnet arrangement may bepositioned above the illustrated portion of the rotor 504 such that thestator segment 208 may be positioned within a gap between the two rotorportions, with lines of magnetic flux extending in a direction parallelto the axis of rotation of the rotor between pairs of opposing, oppositepolarity magnets. In addition, although not illustrated in FIG. 5 , itshould be appreciated that the stator segment 208 may include conductivetraces and/or vias, e.g., disposed on one or more dielectric layers,that are configured to form windings that, when energized with current,generate magnetic flux in a direction parallel to the axis of rotationof the rotor. Such windings may be configured to receive one or morephases of current from a power supply (not shown in FIG. 5 ), and may bearranged in one or more spirals, one or more serpentine patterns, orotherwise, so as to generate such magnetic flux.

As shown in FIG. 5 , in some embodiments, the stator segment 208 may beheld in place via an arcuate attachment member 510 to which the statorsegment 208 may be attached using one or more fasteners 512, and the oneor more windings (not illustrated) of the stator segment 208 may beconnected to terminals 514 associated with the attachment member 510,which terminals may be connected to a controller (not shown in FIG. 5 ),such as the controller 112 discussed above in connection with FIGS. 1Aand 1B, so as to supply energizing current(s) to the winding(s).

FIG. 6 shows the same configuration as FIG. 5 , but with the rotor 504positioned at an angle where the stator segment 208 overlaps with thedense magnet section 506 that provides peak torque.

FIG. 7 shows an alternate arrangement to FIGS. 4 and 5 . As shown, inaddition to or in lieu of employing less dense magnet regions 508 (notshown in FIG. 7 ) together with a dense angular extent 506, statorsegments 208 a-g may be arranged so that they fully or nearly describean annular stator with constant available torque at any angle. In someembodiments, a subset of the stator segments 208 a-g may be madesmaller, may be arranged with a coarser pitch, may contain fewer winding“turns,” and/or may be supplied with less power than one or more otherstator segments 208, so that a machine with concentrated magnets canoffer angle-specific peak torque, while still providing torquecapability at any angle. For example, in some embodiments, the statorsegment 208 a may be configured, arranged and/or energized differentlythan the other stator segments 208 b-g for such a purpose.

No matter the particular arrangement of magnet(s) 502 and statorsegment(s) 208 that is employed, in at least some circumstances, caremay be taken to ensure that at least one stator segment 208 at leastpartially overlaps at least one magnet 502 at each position during arevolution of the rotor 504, so that the rotor 504 does not become“stuck” at a position where no magnetic flux from a stator segment 208interacts with magnetic flux from a magnet 502.

In each of the above-described example configurations, the statorsegment(s) 208 and/or the magnet(s) 502 of the rotor 504 are configuredto have a magnetic flux profile that is non-uniformly distributed aboutthe machine's principle axis of rotation. In particular, the statorsegment(s) 208 are arranged such that, at any given point in time whenthe windings of the stator are energized with current, the locations ofpeak magnetic flux generated by the stator are non-uniformly distributedwith respect to angle about the rotor's axis of rotation. Similarly, insuch machines, the magnets 502 of a rotor 504 are also arranged suchthat, at any given point in time, the locations of peak magnetic fluxgenerated by the rotor are likewise non-uniformly distributed withrespect to angle about the rotor's axis of rotation. Accordingly, foreach of the rotor and the stator in such machines, different anglesseparate at least some locations of peak magnetic flux from adjacentlocations of peak magnetic flux about the axis of rotation so that thatmagnetic flux profile generated by such component is non-uniformlydistributed about the axis of rotation.

FIG. 8 illustrates a cross section of an example embodiment of an axialflux motor 802 that is configured with components like those shown inFIGS. 5 and 6 and that is integrated with a washing machine load 804 inaccordance with some aspects of the present disclosure. As shown, astator segment 208 of the motor 802 may be secured to a housing 806containing a washing machine tub 808 via an attachment member 510 andone or more fasteners 512, and the washing machine tub 808 may berotatably couple to the housing 806 via bearing elements 810. A rotor504 of the motor 802 may directly drive the washing machine tub 808 viaa shaft 812 that may extend from and/or be fixedly attached to thewashing machine tub 808. With the illustrated configuration, continuousrotation at relatively high speed and low torque in “spin” mode may beachieved using the stator segment 208 and a collection of magnets 502arranged into a dense magnet region 506 and one or more less densemagnet regions 508, as described above in connection with FIGS. 5 and 6. During such a spin mode, due to the non-uniform distribution of themagnetic flux profiles of the rotor and the stator about the rotor'saxis of rotation, as the rotor 504 rotates through a range of angleswith respect to the stator segment 208 at a substantially constantspeed, the periodicity of the torque produced due to interaction betweenthe magnetic flux generated by the rotor and the stator is irregular.The reversing action needed for “wash” mode may be a relatively lowspeed, high-torque mode of operation where torque can be supplied atspecific angles. In this case, the interaction of the stator segment 208with the dense magnet region 506 may provide the peak torquerequirement.

Examples Implementations of Apparatuses and Methods in Accordance withthe Present Disclosure

The following paragraphs (A1) through (A14) describe examples ofapparatuses that may be implemented in accordance with the presentdisclosure.

(A1) A motor or generator may comprise a rotor having an axis ofrotation and configured to generate first magnetic flux parallel to theaxis of rotation, and a stator configured to generate second magneticflux parallel to the axis of rotation, wherein at least one of the rotoror the stator is configured to generate a magnetic flux profile that isnon-uniformly distributed about the axis of rotation.

(A2) A motor or generator may be configured as described in paragraph(A1), and the rotor may be further configured to generate a firstmagnetic flux profile that is non-uniformly distributed about the axisof rotation.

(A3) A motor or generator may be configured as described in paragraph(A2), and the rotor may further comprise one or more magnet segmentsnon-uniformly distributed about the axis of rotation.

(A4) A motor or generator may be configured as described in paragraph(A3), and each of the one or more magnet segments may further have arespective surface location at which the first magnetic flux has amaximum density, and the respective surface locations may benon-uniformly distributed about the axis of rotation.

(A5) A motor or generator may be configured as described in any ofparagraphs (A2) through (A4), and the rotor may be further configuredsuch that, as the rotor rotates through a range of angles with respectto the stator at a substantially constant speed, a periodicity of torqueproduced due to interaction of the first magnetic flux and the secondmagnetic flux is irregular.

(A6) A motor or generator may be configured as described in any ofparagraphs (A2) through (A5), and the stator may be further configuredto generate a second magnetic flux profile that is non-uniformlydistributed about the axis of rotation.

(A7) A motor or generator may be configured as described in paragraph(A1), and the stator may be further configured to generate a magneticflux profile that is non-uniformly distributed about the axis ofrotation.

(A8) A motor or generator may be configured as described in any ofparagraphs (A2) through (A7), and the stator may further comprise one ormore printed circuit board segments non-uniformly distributed about theaxis of rotation.

(A9) A motor or generator may be configured as described in any ofparagraphs (A2) through (A8), and the stator may further comprisesconductive traces arranged on at least one dielectric layer to generatethe second magnetic flux when energized with current.

(A10) A motor or generator may be configured as described in any ofparagraphs (A2) through (A9), and the stator may be further configuredsuch that, at any given time when the conductive traces are energizedwith current, one or more locations of maximum density of the secondmagnetic flux are non-uniformly distributed about the axis of rotation.

(A11) A motor or generator may be configured as described in paragraph(A9) or paragraph (A10), the conductive traces are arranged on the atleast one dielectric layer and coupled to a power source to generatethree phases of the second magnetic flux corresponding to three phasesof current output by the power source.

(A12) A motor or generator may be configured as described in any ofparagraphs (A1) through (A11), and the stator may be further configuredsuch that, as the rotor rotates through a range of angles with respectto the stator at a constant speed, a periodicity of torque produced dueto interaction of the first magnetic flux and the second magnetic fluxis irregular.

(A13) A rotor for use in a motor or generator may comprise a supportstructure, and one or more magnet segments that are supported by thesupport structure and that generate first magnetic flux parallel to anaxis of rotation about which the support structure rotates whenassembled with a stator that generates second magnetic flux parallel tothe axis of rotation, wherein the one or more magnet segments areconfigured and arranged to generate a magnetic flux profile that isnon-uniformly distributed about the axis of rotation.

(A14) A rotor may be configured as described in paragraph A13, and theone or more magnet segments may further include at least a first magnetsegment and a second magnet segment spaced apart from the first magnetsegment, and the first magnet segment may include a larger number ofadjacent magnets than the second magnet segment.

The following paragraphs (M1) through (M5) describe examples of methodsthat may be implemented in accordance with the present disclosure.

(M1) A method may comprise arranging one or more magnetic flux producingwindings of a stator non-uniformly about an axis of rotation of a rotorof an axial flux motor or generator.

(M2) A method may be performed as described in paragraph (M1), whereinarranging the one or more magnetic flux producing windings furthercomprises arranging one or more printed circuit board segments includingthe windings non-uniformly about the axis of rotation.

(M3) A method may be performed as described in paragraph (M1) orparagraph (M2), wherein arranging the one or more printed circuit boardsegments may further comprise arranging the one or more printed circuitboard segments such that, at any given time when the windings areenergized with current, one or more locations of maximum density of thesecond magnetic flux are non-uniformly distributed about the axis ofrotation.

(M4) A method may be performed as described in any of paragraphs (M1)through (M3), wherein the rotor may comprise magnets arrangednon-uniformly about the axis of rotation.

(M5) A method may be performed as described in any of paragraphs (M1)through (M4), wherein arranging the one or more magnetic flux producingwindings may further comprise arranging the one or more magnetic fluxproducing windings such that, as the rotor rotates through a range ofangles with respect to the stator at a constant speed, a periodicity oftorque produced due to interaction of magnetic flux generated by therotor and the stator is irregular.

Having thus described several aspects of at least one embodiment, it isto be appreciated that various alterations, modifications, andimprovements will readily occur to those skilled in the art. Suchalterations, modifications, and improvements are intended to be part ofthis disclosure, and are intended to be within the spirit and scope ofthe disclosure. Accordingly, the foregoing description and drawings areby way of example only.

Various aspects of the present disclosure may be used alone, incombination, or in a variety of arrangements not specifically discussedin the embodiments described in the foregoing and is therefore notlimited in this application to the details and arrangement of componentsset forth in the foregoing description or illustrated in the drawings.For example, aspects described in one embodiment may be combined in anymanner with aspects described in other embodiments.

Also, the disclosed aspects may be embodied as a method, of which anexample has been provided. The acts performed as part of the method maybe ordered in any suitable way. Accordingly, embodiments may beconstructed in which acts are performed in an order different thanillustrated, which may include performing some acts simultaneously, eventhough shown as sequential acts in illustrative embodiments.

Use of ordinal terms such as “first,” “second,” “third,” etc., in theclaims to modify a claim element does not by itself connote anypriority, precedence or order of one claim element over another or thetemporal order in which acts of a method are performed, but are usedmerely as labels to distinguish one claimed element having a certainname from another element having a same name (but for use of the ordinalterm) to distinguish the claim elements.

Also, the phraseology and terminology used herein is used for thepurpose of description and should not be regarded as limiting. The useof “including,” “comprising,” or “having,” “containing,” “involving,”and variations thereof herein, is meant to encompass the items listedthereafter and equivalents thereof as well as additional items.

What is claimed is:
 1. A motor or generator, comprising: a rotor havingan axis of rotation and configured to generate a first magnetic fluxparallel to the axis of rotation, wherein a first profile of the firstmagnetic flux is non-uniformly distributed about the axis of rotation;and a stator configured to generate a second magnetic flux, differentthan the first magnetic flux, parallel to the axis of rotation, whereina second profile of the second magnetic flux is non-uniformlydistributed about the axis of rotation.
 2. The motor or generator ofclaim 1, wherein the rotor comprises one or more magnet segmentsnon-uniformly distributed about the axis of rotation, each of the one ormore magnet segments generating a respective portion of the firstmagnetic flux.
 3. The motor or generator of claim 2, wherein each of theone or more magnet segments has a respective surface location at whichthe respective portion of the first magnetic flux generated by thatmagnetic segment has a maximum density, and the respective surfacelocations are non-uniformly distributed about the axis of rotation. 4.The motor or generator of claim 1, wherein the stator comprises one ormore printed circuit board segments non-uniformly distributed about theaxis of rotation.
 5. The motor or generator of claim 1, wherein thestator comprises conductive traces arranged on at least one dielectriclayer to generate one or more respective portions of the second magneticflux when energized with current.
 6. The motor or generator of claim 5,wherein the stator is configured such that, at any given time when theconductive traces are energized with current, one or more locations ofmaximum density of the one or more respective portions of the secondmagnetic flux are non-uniformly distributed about the axis of rotation.7. The motor or generator of claim 6, wherein the conductive traces arearranged on the at least one dielectric layer and coupled to a powersource to generate a rotating magnetic flux corresponding to apoly-phase set of currents output by the power source.
 8. The motor orgenerator of claim 1, wherein the rotor and the stator are configuredsuch that, as the rotor rotates through a range of angles with respectto the stator at a constant speed, a periodicity of torque produced dueto interaction of the first magnetic flux and the second magnetic fluxis irregular.
 9. The motor or generator of claim 1, wherein: the rotorand the stator are configured to provide a torque capability between therotor and the stator that varies aperiodically as a function of anangular position of the rotor relative to the stator as the rotorrotates through a full mechanical rotation about the axis of rotation.10. The motor or generator of claim 1, wherein: the rotor comprises atleast first, second, and third magnets oriented to generate respectiveportions of the first magnetic flux in a first direction parallel to theaxis of rotation; no other magnets that are oriented to generatemagnetic flux in the first direction are positioned angularly betweenthe first magnet and the second magnet; no other magnets that areoriented to generate magnetic flux in the first direction are positionedangularly between the second magnet and the third magnet; and a firstangular distance between the first magnet and the second magnet is atleast two times a second angular distance between the second magnet andthe third magnet.
 11. The motor or generator of claim 10, wherein: thestator comprises at least first, second, and third windings oriented togenerate respective portions of the second magnetic flux in a seconddirection parallel to the axis of rotation when energized with currentof a first polarity; no other windings that are oriented to generatemagnetic flux in the second direction when energized with current of thefirst polarity are positioned angularly between the first winding andthe second winding; no other windings that are oriented to generatemagnetic flux in the second direction when energized with current of thefirst polarity are positioned angularly between the second winding andthe third winding; and a third angular distance between the firstwinding and the second winding is at least two times a fourth angulardistance between the second winding and the third winding.
 12. The motoror generator of claim 1, wherein: a first portion of the rotor isconfigured to generate a first peak magnetic flux density, parallel tothe axis of rotation, at a first location relative to the rotor; asecond portion of the rotor is configured to generate a second peakmagnetic flux density, parallel to the axis of rotation, at a secondlocation relative to the rotor; a first portion of the stator isconfigured to generate a third peak magnetic flux density, parallel tothe axis of rotation, at a third location relative to the stator; andthe rotor and the stator are configured such that a first torquecapability between the rotor and the stator when the first location isangularly aligned with the third location is greater than a secondtorque capability between the rotor and the stator when the secondlocation is angularly aligned with the third location.
 13. The motor orgenerator of claim 12, wherein: the rotor and the stator are configuredsuch that the first torque capability when the first location isangularly aligned with the third location is at least twenty fivepercent greater than the second torque capability when the secondlocation is angularly aligned with the third location.
 14. The motor orgenerator of claim 12, wherein: the rotor and the stator are configuredsuch that the first torque capability when the first location isangularly aligned with the third location is at least two times thesecond torque capability when the second location is angularly alignedwith the third location.
 15. The motor or generator of claim 1, wherein:a first portion of the stator is configured to generate a first peakmagnetic flux density, parallel to the axis of rotation, at a firstlocation relative to the stator; a second portion of the stator isconfigured to generate a second peak magnetic flux density, parallel tothe axis of rotation, at a second location relative to the stator; afirst portion of the rotor is configured to generate a third peakmagnetic flux density, parallel to the axis of rotation, at a thirdlocation relative to the rotor; and the rotor and the stator areconfigured such that a first torque capability between the rotor and thestator when the first location is angularly aligned with the thirdlocation is greater than a second torque capability between the rotorand the stator when the second location is angularly aligned with thethird location.
 16. The motor or generator of claim 15, wherein: therotor and the stator are configured such that the first torquecapability when the first location is angularly aligned with the thirdlocation is at least twenty five percent greater than the second torquecapability when the second location is angularly aligned with the thirdlocation.
 17. The motor or generator of claim 15, wherein: the rotor andthe stator are configured such that the first torque capability when thefirst location is angularly aligned with the third location is at leasttwo times the second torque capability when the second location isangularly aligned with the third location.
 18. The motor or generator ofclaim 1, wherein: the rotor comprises a plurality of magnets configuredand arranged to generate the first magnetic flux, wherein the pluralityof magnets are arranged such that a first angular half of the rotorgenerates a first portion of the first magnetic flux and a secondangular half of the rotor generates a second portion of the firstmagnetic flux that is substantially greater than the first portion. 19.The motor or generator of claim 1, wherein: magnets that generate thefirst magnetic flux are arranged with 1-fold angular symmetry withrespect to the rotor.
 20. The motor or generator of claim 1, wherein:one or more portions of the rotor are configured to generate peakmagnetic flux densities in a first direction parallel to the axis ofrotation at one or more first angular locations of a first angular halfof the rotor and at zero or more second angular locations of a secondangular half of the rotor, wherein a quantity of the one or more firstangular locations is greater than a quantity of the zero or more secondangular locations.
 21. The motor or generator of claim 20, wherein: oneor more portions of the stator are configured to generate peak magneticflux densities in a second direction parallel to the axis of rotation atone or more third angular locations of a first angular half of thestator and at zero or more fourth angular locations of a second angularhalf of the stator, wherein a quantity of the one or more third angularlocations is greater than a quantity of the zero or more fourth angularlocations.
 22. The motor or generator of claim 1, wherein: a firstangular half of the rotor includes a first quantity of magnets orientedto generate respective first portions of the first magnetic flux in afirst direction parallel to the axis of rotation; a second angular halfof the rotor includes a second quantity of magnets oriented to generaterespective second portions of the first magnetic flux in the firstdirection; and the first quantity is greater than the second quantity.23. The motor or generator of claim 22, wherein: a first angular half ofthe stator includes a third quantity of windings oriented to generaterespective first portions of the second magnetic flux in a seconddirection parallel to the axis of rotation when energized with currentof a first polarity; a second angular half of the stator includes afourth quantity of windings oriented to generate respective secondportions of the second magnetic flux in the second direction whenenergized with current of the first polarity; and the third quantity isgreater than the fourth quantity.
 24. The motor or generator of claim 1,wherein: the rotor comprises one or more magnets configured to generatethe first magnetic flux, wherein the one or more magnets arenon-uniformly distributed about the axis of rotation; and the statorcomprises one or more windings that, when energized with current,generate the second magnetic flux, wherein the one or more windings arenon-uniformly distributed about the axis of rotation.